I've revived the above texts from my friend simply called "me". Apparently the text messages tell you everything you need to know. Arrrrrrgh! I told him not to mess with people.
The kidnapper is a card game.
Count the number of consecutive letters. For example,
Continue this then you get:
9 13 9 14 4 3
We might get a message here...
Perform A1Z26 cipher: IMINDC $\rightarrow$ I'M IN DC
Does it mean you are in Washington, DC?
Building off u_ndefined's answer:
The person is in Washington D.C.
Where the king stays:
The King, aka Elvis Presley is prominently on display at the Smithsonian National Museum of American History
The one who kills our children:
Elvis is famous for revolutionizing the minds of America's youth thus, "killing" the children from the perspective of former generations. According to wikipedia:
Presley, more than anyone else, gave the young a belief in themselves as a distinct and somehow unified generation—the first in America ever to feel the power of an integrated youth culture.